The Functions of Operating Systems Spooling

Learning Objectives Describe spooling, explaining why it is used.

Simultaneous Peripheral Operations On-Line (spooling) Temporarily stores all input and output jobs on some form of backing storage (usually a high-speed device such as a disk), with a reference to the job and its location stored on a spool / print queue. When the output from a job is finished, the name location of the file can be placed in a queue. The Spooler / Print spooler (part of the OS) can now send the name and location of the file to the printer in the order in which the file details enter the queue. Then the printer pulls them off the backing storage device at its own rate.

Reason for Spooling So that slow peripheral devices do not hold up the processor. I/O devices are relatively slow when compared to the processor. I/O devices are relatively slow when compared to the processor.

Why spool in the way we do? Jobs are named and not listed in the printer queue until the entire job has been saved: Spooling compensates for the speed mismatch between the processor and input/output devices; input/output devices cannot process jobs as fast as they are sent by a processor. Spooling ensures that when, multiple jobs sent at the same time to a single device are queued, they are kept separate, no jobs are lost and complete jobs are processed. Spooling ensures that when, multiple jobs sent at the same time to a single device are queued, they are kept separate, no jobs are lost and complete jobs are processed.

Process of sending jobs for printing using a spooler Jobs are stored temporarily on some form of backing storage (usually a high-speed device such as a disk). When storage of a job is complete, its location is stored on a spool / print queue. The jobs in the spool queue can be prioritized and a job reference can enter the queue at a position according to its priority.

Spooler or Print Spooler The part of the OS that handles the task of spooling.

Example Two jobs, in a network system, are producing output that is to go to a single printer. The output is being produced in sections and must be kept separate for each job. Opening two files (File1 and File2) on a disk, one for each job, can do this. As the files are on disk, job 1 can write to File1 whenever it wishes and job 2 can write to File2. When the output from a job is finished, the name (and other details) of the file can be placed in a queue. OS can now send the output to the printer in the order in which the file details enter the queue. As the name of a file does not enter the queue until all output from the job to the corresponding file is complete, the output from different jobs is kept separate.

Notes: Spooling can be used for any number of jobs. Output itself is not placed in the queue. The queue simply contains the details of the files that need to be printed so that the spooler can send these details to the printer so that it can retrieve them at its own rate.

Simultaneous Peripheral Operations On-Line (spooling)

Plenary Describe the process of spooling when sending jobs for printing.

Process of sending jobs for printing using a spooler Jobs are stored temporarily on some form of backing storage (usually a high-speed device such as a disk). When storage of job complete the job and its location are stored on a spool / print queue. The jobs in the spool queue can be prioritized and a job reference can enter the queue at a position according to its priority.